1. Field of the Invention
The present invention relates to a two-domain in-plane switching mode liquid crystal display (IPS-LCD) and, more particularly, to an electrode array of the IPS-LCD to generate a gradient electric field between a pixel electrode and a common electrode.
2. Description of the Related Art
In-Plane Switching mode liquid crystal display (IPS-LCD) has been used or suggested in wide view angle display technology to improve a conventional twisted nematic (TN)-LCD. The IPS-LCD has common electrodes and pixel electrodes formed on a lower glass substrate (TFT substrate) and an in-plane electrode field therebetween is generated to rearrange the LC molecules along the electrode field. Accordingly, the IPS-LCD device can improve viewing angle, contrast ratio and color shift over the conventional twisted nematic device.
Depending on the electrode array of the common electrodes and the pixel electrodes, the IPS-LCD is classified into a single-domain type and a two-domain type. FIG. 1 is a top view showing an electrode array of a conventional single-domain IPS-LCD 10. Two parallel gate lines 2 are orthogonal to two parallel data lines 4 to define a rectangular-shaped pixel area, in which a TFT device 5, a comb-shaped pixel electrode 6 and a herringbone-shaped common electrode 8 are formed. The center wiring 8a of the common electrode 8 transversely extends along the center of the pixel area, and the bones 8b of the common electrode 8 lengthwise extend form the center wiring 8a. The teeth 6a of the pixel electrode 6 are disposed in the intervals of the bones 8b. When an outer voltage is applied to the IPS-LCD, an in-plane electric field is generated between the adjacent bone 8b and tooth 6a. 
The strip-shaped teeth 6a are parallel to the strip-shaped bones 8b, thus the in-plane electric field generated between the adjacent bone 8b and tooth 6a is uniform. The uniform electric field indicates that the differential (or gradient) of the strength (including direction) of the electric field at each point to the corresponding planar space is zero. This can make LC molecules have a uniform driving state at the same time, but this needs a higher driving voltage. A way to solve this problem is to reduce the distance between the adjacent bone 8b and tooth 6a by increasing the number of the teeth 6a and the bones 8b in the pixel area to lower the driving voltage of the IPS-LCD 10. However, the line width of the teeth 6a and bones 8b cannot be narrower than about 3 to 4 microns, thus the aperture ratio of the pixel area is decreasing as the number of the teeth 6a and the bones 8b is increasing. The single-domain IPS-LCD 10 with the above-described array design of a uniform electric field cannot simultaneously give consideration to the requirements of high aperture ratio and low driving voltage.
A two-domain IPS-LCD is developed for solving a problem of color shift of the single-domain IPS-LCD 10. FIG. 2 is a top view showing an electrode array of a conventional two-domain IPS-LCD 20. Two transverse-extending gate lines 12 and two lengthwise-extending data lines 14 define a pixel area 11, in which a TFT device 15, a comb-shaped pixel electrode 16 and a herringbone-shaped common electrode 18 are formed. Each of the teeth 16a of the pixel electrode 16 and the bones 18b of the common electrode 18 has a chevron-shaped profile and the inclined portion of the chevron-shaped profile is parallel to the adjacent electrode. When an outer voltage is applied to the IPS-LCD 20, the directions of the electric fields at two sides of the center wiring 18a are different to make a part of LC molecules rotate in a counterclockwise direction and another part of LC molecules rotate in a clockwise direction. Therefore, the center wiring 18a demarcates the pixel area 11 as an upper single-domain area 11a and a lower single-domain area 11b. Within each single-domain area 11a or 11b, the inclined portion of the tooth 16a is parallel to the inclined portion of the bone 18b and thus a uniform in-plane electric field is generated therebetween. This still encounters the problems of high driving voltage and low aperture ratio.
FIG. 3 is a top view showing the rotation of LC molecules in a uniform electric field of a conventional multi-domain IPS-LCD 30. In a pixel area, three pixel electrodes 24a, 24b and 24c are disposed in the intervals of four common electrodes 26a, 26b, 26c and 26d between two adjacent data lines 22. Each of the data lines 22, the pixel electrodes 24 and the common electrodes 26 has a specific profile that is formed by lengthwise connecting at least two xe2x80x9c less than xe2x80x9d shapes. In addition, an orientation layer is formed to cover the pixel area and rubbed in a direction shown as arrow A. When no outer voltage or an outer voltage below the threshold voltage is applied to the IPS-LCD 30, LC molecules 28 are aligned along the direction shown as arrow A.
Hereinafter, a single-domain area between the pixel electrode 24b and the common electrode 26b is an example of how the first LC molecule 28I adjacent to the tip of the xe2x80x9c less than xe2x80x9d shape and the second LC molecule 28II far away from the tip of the xe2x80x9c less than xe2x80x9d shape rotate. When an outer voltage is applied to generate an in-plane electric field that is lager than a threshold electric field, the directors of the first LC molecule 28I and the second LC molecule 28II rotate uniformly to become the LC molecules 28Ixe2x80x2 and 28IIxe2x80x2, respectively. Since the rotating angles, depending on the degree of the applied voltage, of the first LC molecule 28I and the second LC molecule 28II are the same, the rotated LC molecules 28Ixe2x80x2 and 28IIxe2x80x2 are parallel to each other. That is, the first LC molecule 28I and the second LC molecule 28II simultaneously start rotating, simultaneously stop rotating, and have the same rotating angle. There is no rotating moment generated between the first LC molecule 28I and the second LC molecule 28II, and no elastic distorted energy existed between the first LC molecule 28I and the second LC molecule 28II. Further, if the applied voltage is smaller than the threshold electric field, all the LC molecules 28 positioned in the single-domain area cannot rotate because they have the same threshold electric field. This still encounters the problems of high driving voltage and low aperture ratio.
The present invention is to provide an electrode array of a two-domain IPS-LCD to solve the problem caused by the prior art.
In the IPS-LCD, a plurality of lengthwise-extending common electrodes is formed in each pixel area, and each common electrode has a curved profile. A plurality of lengthwise-extending pixel electrodes are formed in each pixel area, and each pixel electrode has a curved profile. The pixel electrodes are disposed it the intervals of the common electrodes, and two adjacent pixel electrode and common electrode form a sub-pixel area. Liquid crystal molecules are positioned within each sub-pixel area where is defined as at least two single-domain areas according to the rotating direction of the liquid crystal molecules. The two adjacent pixel electrode and common electrode within each sub-pixel area are not parallel to each other, thus a gradient in-plane electric field is generated therebetween.
Accordingly, it is a principal object of the invention to provide an IPS-LCD with a lower driving voltage without reducing aperture ratio.
Yet another object of the invention is to provide an IPS-LCD with a gradient electric field within a single-domain area.
It is a further object of the invention to provide an IPS-LCD to decrease the turn-on time.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.